In the field of transportation and shipment of goods, xe2x80x9cdunnage bagsxe2x80x9d are frequently used. Dunnage bags are inflatable structures, typically inflated with pressurized gas, designed to be disposed in the void spaces of a cargo container or hold.
It is well conventionally practiced in the field of cargo transportation to place dunnage bags between individual, adjacent cargo pieces, or between the individual cargo pieces and the side walls of a cargo container or hold, to fill the voids within the container or hold and thereby prevent damage to the cargo pieces or walls of the container or hold due to shifting of cargo during transportation. Because dunnage bags are subjected to forces of cargo attempting to shift, they must be resistant to rupturing or leakage in an environment where the surface of the bag will be subject to abrasion, contact with edges and corners, etc.
Previously known dunnage bags typically consist of three major components, an inflatable bladder, an outer covering and some means to inflate and/or deflate the bladder. The inflatable bladder typically consists of a sac of gas-impervious, flexible and relatively elastic material such as rubber, thermoplastic material (such as polyethylene) or the like. Surrounding the inflatable bladder is the outer covering, which typically consists of an outer bag composed of a sturdy, relatively inelastic material such a canvas, nylon or multiple layers of kraft paper. The general purposes of the outer covering is twofold, to prevent over-expansion and rupture of the inflatable liner and provide a sturdy covering which protects the inflatable bladder from damage due to abrasion, edges and corners. Finally, some means of at least inflating the inner bladder of the bag is provided, typically a one-way or check valve disposed in the wall of the bag.
The prior art has generally directed its attention to providing dunnage bags having specific constructions which either increase the strength of the bag or decrease the cost of manufacturing and/or using same.
The first dunnage bags were intended for extensive reuse. As such they were typically comprised of a heavy, durable inner bladder, such as rubber, and a heavy, durable outer covering such as canvas. Later, inner bladders and outer coverings of differing materials, such as polyethylene bladders and nylon outer coverings were used. But such bags were possessed of several disadvantages. Because of their construction such bags were heavy, expensive to manufacture, and if to be reused (which their cost nearly mandated) had to be deflated (which was time consuming and could rarely be accomplished fully with the bag in the cargo container), handled carefully, carefully packed for return to the shipper, etc. Accordingly, time, trouble and cost of using such bags was found to be prohibitively high.
In an attempt to reduce cost of dunnage bags the prior art next turned a form of disposable bag which employed a tube of gas impervious material (such as polyethylene) inside of a tube of multiple layers of more resilient material, such as kraft paper, the ends of which tube was sealed by reusable rods and clamps. This solution had several disadvantages. Manufacture of the sleeve of gas impermeable liner within a sleeve of multiple layers of more resilient material remained expensive. Also, metal clamps were expensive, were prone to leak in transit and unless positioned carefully were themselves capable of damaging dunnage bags, the cargo or its container and had to be returned to a shipper for reuse. Also, while in theory the bladder material and outer material could be separated into different streams and each separately recycled, because of the cost of labor involved in separation, used bags were frequently disposed, creating waste disposal issues.
Because of the inherent problems associated with earlier dunnage bags, later emphasis was placed on bags which were intended to be used once and disposed. As bags of this type were intended to be used only once the art endeavored to construct these bags so as to minimize the cost manufacture. A general result of this effort has been the evolution of a dunnage bag wherein the inner bladder bag consists of a relatively thin-walled thermoplastic material, such as polyethylene, which is disposed in an outer covering which consists of multiple layers of kraft paper (sometimes called xe2x80x9ccardboardxe2x80x9d), the ends of which are permanently sealed by an adhesive. With a dunnage bag construction of this type, the bladder serves mainly as a gas tight member while the plurality of paper sheets provide the requisite resistance to bursting, abrasion and puncture.
Such bags nevertheless have various disadvantages. They are still relatively expensive to manufacture and use. In practice they are made by first forming a thin sleeve of thermo-plastic material which will become the inflatable bladder of the bag. Then that sleeve is typically moved along an assembly line where it is wrapped with multiple layers of kraft paper which are overlapped circumferentially and glued together longitudinally forming a sleeve. In general, the greater the gas pressure the bag is designed to hold, the more layers of paper will be applied. Thereafter a desired length of the sleeve, now comprising multiple layers of kraft paper having an inner sleeve of gas impervious material, is cut to a desired length, a gas valve installed in the wall of the sleeve, and the ends of the sleeves sealed, typically by application of adhesive and folding.
Inasmuch as outer layers of such bags, which give the bag most of its resistance to bursting, abrasion or puncture, consists of paper, such bags are susceptible to moisture, and while such bags are designed to be disposed of after single use, disposal is a problem. While in theory the paper and the plastic components of the bags could be at least largely be separated and recycled appropriately, in practice that is almost never done because of labor costs involved, and separation would likely be incomplete even if attempted, because the ends of the bladder are typically glued into folds of the paper. Hence near major receiving centers disposal of dunnage bags creates waste disposal issues.
Various dunnage bag constructions of prior art are disclosed in U.S. Pat. Nos. 3,426,891; 3,442,402; 3,556,318; 3,868,026; 4,040,526; 4,553,887; 4,591,519; 5,288,188; 5,339,602; 5,437,301; 5,788,438 and 5,908,275.
The bag and method of manufacture herein disclosed is designed to address some of the disadvantages discussed above.
A principal object of the present invention is to provide a dunnage bag which has the advantages of bags of prior art, that is be capable of being inflated with and retaining gas pressure, be resistant to bursting, abrasion and puncture from edges and corners of goods, but be more economical to manufacture, have an improved strength to weight ratio, be moisture resistant, may be reused if desired and be facilely recyclable.
To these ends the objects of the invention are to provide a gas impervious dunnage bag which is comprised of low cost materials, is easily manufactured, is burst resistant, has an outer surface resistant to bursting, abrasion and damage from edges and corners of goods, is moisture resistant, is reusable and is readily recyclable.
Another object of the invention is to provide a dunnage bag, the wall of which is comprised of an outer layer of woven strips of strong thermoplastic polymeric material which is resistant to moisture, bursting, abrasion or damage by cargo edges and corners and a continuous inner layer of gas impervious thermoplastic polymeric material integrally fused to said outer layer and is therefore sturdy, lightweight, easy and economical to use, reuse and/or recycle.
Another object of the invention is to provide a bag the ends of which are sealed in a manner which is resistant to stretching, tearing, unraveling, bursting abrasion, damage by contact with cargo and is moisture resistant.
Yet other objects of the invention relate to providing a method of manufacturing the dunnage bag of the present invention in a rapid, economical and efficient manner.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art when the following description of the preferred embodiments is read in conjunction with the accompanying drawings.
The above and further objects are achieved in accordance with the present invention wherein there is provided a recyclable dunnage bag for cushioning pieces of cargo during shipment, where the wall of the dunnage bag includes an inner layer comprised of a continuous film of a gas impervious polymer, which inner liner is integrally fused to the interior of an outer layer of durable woven polymer, and has a means for inflation of said dunnage bag.
Forming the dunnage bag begins with a sleeve, preferably seamless, of woven thermoplastic polymer selected for characteristics of strength, resistance to moisture, abrasion and damage by edges and corners of cargo. Then preferably to the outer surface of the sleeve a continuous layer of thermoplastic polymer selected for gas impermeability, moisture resistance and compatibility with said woven polymer is integrally fused, preferably by extrusion of a layer of molten polymer onto the surface of the woven polymer and hot compression thereto, preferably by pinch rolling. Then a desired length of the sleeve is cut, if necessary turned xe2x80x9cinside-outxe2x80x9d so that the woven thermoplastic polymer is on the outside of the sleeve and the continuous layer of thermoplastic polymer is on the inside of the sleeve. Then the ends of the sleeve are sealed by thermal fusion, gluing, folding and/or securing of the folds to the exterior of the dunnage bag. Either before or after reversal of the sleeve a means for admitting gas, which is preferably a xe2x80x9ccheckxe2x80x9d or one-way valve means, is installed in the wall of the bag.